Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. One example of a disk drive is a hard disk drive. A conventional hard disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk, and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider towards the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of the moving air.
When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a program to implement writing and reading functions.
Perpendicular magnetic recording (PMR) writers are now being utilized in write heads to increase the data density of hard disk drives. Such PMR writers record magnetic bits of data in a direction that is perpendicular to the surface of the magnetic disk. A PMR writer generally includes a write pole having a relatively small cross sectional surface at the air bearing surface (ABS) and a return pole having a larger cross sectional surface at the ABS. A magnetic write coil induces a magnetic flux to be emitted from the write pole in a direction generally perpendicular to the plane of the magnetic disk.
Traditionally, a PMR write pole is defined and fabricated using one-step photolithography and a subsequent reactive ion etch or ion-mill. FIGS. 1A-1E show a conventional PMR fabrication process using one-step photolithography.
FIG. 1A shows a top view and a cross-sectional view of a multi-layer structure comprising a substrate 110, an insulator layer 115 and a photoresist layer 120. The photoresist layer 120 is patterned to form a nose pattern in the photoresist layer 120 using one-step photolithography with one photo mask 210 (shown in FIG. 2A). The nose pattern comprises a pole pattern and a yoke pattern that tapers downward to the pole pattern. Due to the optical proximity effect, the corners 125 of the nose pattern are rounded, as shown in the top view in FIG. 1A.
In FIG. 1B, a ruthenium (Ru) layer 130 is deposited over the photoresist layer 120. In FIG. 1C, the Ru layer 130 on the sides of the photoresist layer 120 is removed using side milling. In FIG. 1D, the photoresist layer 120 and the Ru 130 layer on the top of the photoresist layer 120 are lifted off to transfer the nose pattern from the photoresist layer 120 to the Ru layer 130. As shown in the top view in FIG. 1D, the nose pattern transferred to the Ru layer 130 includes rounded corners 135 corresponding to the rounded corners 125 in the photoresist layer 120.
In FIG. 1E, the patterned layer Ru 130 is used as a hard mask for a reactive ion etch (RIE) to form a trench 140 in the insulator layer 115. The trench 140 includes a yoke trench and a pole trench. In a subsequent step, the trench 140 in the insulator layer 115 is filled with a magnetic material (not shown). The magnetic material in the pole trench forms a write pole.
In a later process, a portion of the write pole is lapped off to form a cross sectional surface at the ABS that faces the magnetic disk and though which magnetic flux flows from the write pole to the magnetic disk for writing data to the magnetic disk. The write pole is lapped along a plane that is perpendicular to the top view in FIG. 1E.
New generation PMR writers require very short nose lengths with no nose shape rounding and zero chisel angle at ABS to ensure high write performance and to reduce variations in write performance from device to device. Conventional PMR fabrication processes are unable to meet this require because of nose shape rounding due to the optical proximity effect.